Preparation and application of 3-methoxycatechol modified reduced graphene oxide composite material

Abstract

The invention discloses a preparation method of a 3-methoxy catechol modified reduced graphene oxide composite material, which comprises the following steps: by using reduced graphene oxide as a conductive substrate through a non-covalent functionalization strategy, selecting reversible electrochemical active organic phenol, and adopting a solvothermal self-assembly method, fixing the reversible electrochemical active organic phenol on the surface of the reduced graphene oxide to obtain the 3-methoxy catechol modified reduced graphene oxide composite material. An organic molecule non-covalent functionalized graphene composite electrode material is prepared, the actual energy storage performance of the organic molecule non-covalent functionalized graphene composite electrode material is researched, and the composite electrode material MOC-rGO is prepared from 3-methoxycatechol and reduced graphene oxide through a non-covalent pi-pi effect. The composite electrode material has good rate capability and cycling stability, and in addition, an asymmetric supercapacitor (HAQ-rGO / / MOC-rGO) formed by MOC-rGO and HAQ-rGO has excellent energy storage performance.

Description

Technical Field

[0001] The invention relates to a method for preparing a 3-methoxycatechol-modified reduced graphene oxide composite material, which is mainly used as a positive electrode material for preparing a supercapacitor and belongs to the technical field of composite materials and the technical field of electrochemistry. Background Art

[0002] The global population is growing, and the burning of fossil fuels has increased the content of greenhouse gases in the atmosphere, leading to global warming, forcing people to find and turn to renewable energy. The demand for energy storage in daily life is growing, so more and more portable electronic products and new energy storage devices are born out of need. Among various energy storage devices, supercapacitors, as a new type of electrochemical energy storage device, have the advantages of high power density, good cycle performance, fast charge and discharge rate, long cycle life, and wide temperature adaptability. The energy density of supercapacitors is closely related to the electrode material. Therefore, the selection of electrode materials is crucial to improve the energy density. Graphene, as a 2D carbon nanomaterial, has been a hot topic in the field of supercapacitors since its discovery because of its good conductivity and high specific surface area. Graphene nanosheets self-assemble to form graphene aerogels with a three-dimensional (3D) network structure. The 3D structure effectively prevents the agglomeration between graphene nanosheets, accelerates the charge migration between the electroactive material and the conductive substrate, and is also conducive to the migration and penetration of electrolyte ions, greatly shortening the diffusion path, thereby promoting rapid electrochemical reactions and showing excellent electrochemical performance.

[0003] Organic small molecules with electrochemical activity and reversibility are considered as potential electrode materials for supercapacitors due to their low price, recyclability and wide availability. Combining organic molecules with conductive substrate graphene (rGO) is an effective way to improve the conductivity of organic molecules. Converting graphite oxide (GO) into functionalized graphene by covalent and non-covalent functionalization methods and suitable surface modifiers has been shown to be an effective method to adjust the structure and morphology of graphene and can be used to prepare high-performance electrode materials in SCs. However, covalent functionalization produces strong bonds between graphene nanosheets and organic molecules, and the carbon bonding sites are converted from sp 2 becomes sp 3 This connection causes the p electrons in the carbon atoms in graphene to be removed, and the carrier density is reduced. However, non-covalent functionalization has little effect on the graphene π-π bonding system. Most covalent functionalization methods lead to a decrease in the conductivity of graphene, while the conductivity of graphene can still be maintained when non-covalent functionalization is used. Therefore, non-covalent functionalization of graphene has obvious advantages in reducing the charge transfer resistance between organic molecules and conductive substrates and maintaining the conductivity of materials. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a 3-methoxycatechol modified reduced graphene oxide composite material, which effectively compounds a double electric layer material (graphene) and a pseudocapacitor material (phenolic organic molecule) through non-covalent functionalization, and utilizes the positive synergistic effect of the two to improve the charge storage capacity of the graphene material. In addition, the phenolic graphene composite material prepared by a green, economical and simple solvothermal method has a self-supporting 3D porous structure, can create new pores of different sizes, can alleviate graphene aggregation and restacking, and enhance the ion and electron transmission capacity, thereby improving the electrochemical performance of supercapacitors.

[0005] 1. Preparation of 3-methoxycatechol-modified reduced graphene oxide composites The preparation method of the 3-methoxycatechol (MOC) modified reduced graphene oxide composite material of the present invention comprises the following steps: firstly dispersing graphene oxide in double distilled water to obtain a graphene oxide dispersion, then mixing 3-methoxycatechol and ethanol, then adding the graphene oxide dispersion and mixing evenly, then transferring the mixed solution to a stainless steel high-pressure reactor, heating the mixture to 175-185° C. to react for 10-14 hours, and after the temperature drops to room temperature, washing and freeze-drying are performed to obtain the 3-methoxycatechol modified reduced graphene oxide composite material, which is recorded as MOC-rGO.

[0006] The mass ratio of 3-methoxycatechol to graphene oxide is 0.1:1~0.3:1; and freeze drying is performed at -50~-20°C for 12~48h.

[0007] As a control, reduced graphene oxide rGO was prepared by the same procedure without adding MOC.

[0008] Figure 1 This is a schematic diagram of the synthesis of MOC-rGO composite materials. In this experiment, MOC was first dissolved in ethanol (C 2 H 5 OH), and then add it to the GO dispersion. Since the solvothermal condition can increase the interaction between the solvent molecules and the graphene surface, reduce the potential energy barrier of the solvent molecules, and effectively diffuse into the interlayer to achieve the exfoliation effect, the solvothermal technology is used to make H 2 O / C 2 H 5The OH mixed solvent effectively diffuses into the GO nanosheet layer to achieve the peeling effect and then disperses this layer. In addition, the solvent thermal environment can cause dehydroxylation and induce GO to recover π conjugation. In the one-step solvent thermal reduction process of GO, the transformation from GO to rGO is achieved through non-covalent π-π interaction, electrostatic interaction, hydrogen bonding and hydrophobic interaction. Under the synergy of π-π interaction and hydrogen bonding, MOC is adsorbed on rGO. For the reaggregation and stacking between GO sheets in a single GO dispersion, the addition of MOC can not only alleviate the re-stacking of GO nanosheets, but also generate abundant new pores, providing a shortcut for the diffusion of electrolyte ions, and finally forming a new type of hydrogel composite electrode material with a three-dimensional hierarchical pore structure. With the good electronic conductivity of rGO, unimpeded high-speed electron transport between MOC and rGO conjugated network can be achieved, achieving the effective superposition of double-layer capacitance and electrochemical capacitance in the electrochemical reaction process, thereby improving the overall electrochemical energy storage performance of the composite electrode material.

[0009] 2. Structural Characterization of Composite Materials The morphological characteristics of the materials were analyzed by scanning electron microscopy (FESEM; Ultra Plus, Germany), and the structural characteristics of the samples were measured by Raman spectra.

[0010] 1. Morphology analysis The morphology and microstructure of the substrate rGO and the composite material MOC-rGO were observed and analyzed by field emission scanning electron microscopy (FESEM). Figure 2 As shown in Figures 2a, 2b, 2c and 2d, both rGO and organic molecule functionalized graphene hydrogel MOC-rGO have obvious three-dimensional connected hierarchical pore network structures, but the self-aggregation of rGO is more obvious and presents a more closely connected dense structure.

[0011] 2. Raman analysis Raman scattering spectra are closely related to electronic structure and are often used to characterize graphene materials. Figure 3 All Raman spectra were obtained at 1330 and 1580 cm -1 There are two ordered characteristic peaks: D peak and G peak. D peak is related to graphene sp 2 The G peak is related to the irregular structural defects or disorder of carbon atoms, while the D peak is related to the in-plane vibration of C atoms in the graphene lattice. The intensity ratio of the D peak to the G peak (I D / I G ) can measure the degree of defects in the sample. After the introduction of MOC, the I D / I GThe ratio decreased slightly, indicating that rGO was non-covalently modified by MOC molecules, the order of the composite material increased, and the graphene sp 2 The conjugated structure is not destroyed. In other words, during the solvothermal process, the organic molecule MOC may play a role in repairing graphene defects to a certain extent.

[0012] 3. Electrochemical Performance Preparation of working electrode: Using glassy carbon electrode (5 mm) as the current collector in the three-electrode system, 4 mg of the prepared sample and 0.7 mg of acetylene black (mass ratio 85:15) were fully ground and ultrasonically dispersed in 0.4 mL Nafion solution (0.25wt%). A uniform dispersion (6 μL) was taken with a pipette and dropped onto the glassy carbon electrode and dried naturally at room temperature. In the two-electrode system, the mass of acetylene black and the sample was increased by 4 times at the same time, and 0.4 mL Nafion solution (0.25wt%) was dripped into the mixture after careful grinding. Ultrasonication was continued at room temperature until the mixed liquid system was uniformly dispersed. Finally, a certain amount of dispersion was dripped onto the glassy carbon electrode and dried naturally for use.

[0013] Electrochemical performance test: A three-electrode system was constructed using a glassy carbon electrode coated with active materials as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. The electrochemical properties of the material were tested by cyclic voltammetry (CV) and constant current charge and discharge (GCD) tests. Cyclic voltammetry (CV) and constant current charge and discharge (GCD) tests were performed in the two-electrode system. All electrochemical tests were performed on a CHI760E electrochemical workstation, and the cycle stability was completed using a LAND battery test system. The electrolyte used was 1 MH 2 SO 4 .

[0014] 1. Electrochemical properties of composite materials We designed and assembled a three-electrode system to evaluate the electrochemical performance of the prepared electrode material MOC-rGO. Figure 4 a is a comparison of the cyclic voltammetry (CV) curves of pure organic molecule MOC, composite MOC-rGO and rGO. In the potential range of -0.4~0.6 V, the CV curve of rGO shows a typical quasi-rectangular shape, indicating the characteristics of the EDLC mechanism.

[0015] Figure 4 b is the potential range of -0.4~0.6 V (vs SCE) for MOC-rGO composite electrode materials, 1 mol•L - 1 H 2 SO 4 In electrolyte, the scan rate is 5~50 mV•s-1 CV curves under . Obviously, with the increase of scan rate, the CV curve of MOC-rGO shows that the MOC-rGO composite electrode material has good rate performance. The oxidation peak and reduction peak also show good symmetry.

[0016] In an acidic electrolyte, 3-methoxycatechol undergoes an electrochemical process in which two electrons and two protons are converted into each other. The corresponding redox reaction is shown below: Figure 4 c is the current density 1 A•g -1 Under the potential window from -0.4 V to 0.6 V, the GCD curves of pure organic molecule MOC, rGO and composite material MOC-rGO. Compared with pure MOC and rGO, MOC-rGO has a pair of clear charge and discharge platforms and is highly symmetrical in the potential-time curve. This shows that the electrochemical reaction of the composite electrode material is a fast and reversible process. At 1A•g -1 Under this condition, the specific capacitance of MOC-rGO is 427.9 F·g -1 , which is higher than rGO (157.4 F·g -1 )、pure MOC(4.3 F•g -1 ) have larger specific capacitance, which is consistent with the result of cyclic voltammetry test.

[0017] 2. Electrochemical performance test of asymmetric capacitors Energy density ( E ) and power density ( P ) is an important parameter for measuring the energy storage and conversion of supercapacitors. In order to test the actual energy storage performance of electrode materials and improve energy density. We chose MOC-rGO material with excellent cycle stability as the positive electrode and HAQ-rGO composite electrode material as the negative electrode to construct an asymmetric capacitor, marked as HAQ-rGO / / MOC-rGO (ASC). The preparation of the negative electrode HAQ-rGO negative electrode material is as follows: 54 mg HAQ is dissolved in 16 mL DMF, and then 54 mL GO dispersion (2.0 mg mL -1 ) was added to the above system, and the mixed solution was ultrasonically treated for 1 h and then transferred to a high-pressure reactor for continuous reaction at 180 °C for 12 h. After the reaction was completed, it was naturally cooled to room temperature, and the hydrogel was taken out with tweezers, fully soaked with sufficient deionized water, washed repeatedly, and finally freeze-dried to obtain HAQ-rGO dry gel.

[0018] Since the energy density is proportional to the cell voltage (ΔV), we widened ΔV to the maximum extent and tested the CV curve of the capacitor at different operating voltages. The results showed that when the operating voltage increased from 1.0 V to 1.6 V, no hydrogen and oxygen evolution phenomena were observed in the CV curve. Therefore, the operating voltage of the capacitor was determined to be 1.6 V. Figure 5 a is the ASC at 0−1.6 V, scan rate 10-100 mV•s -1 As can be seen from the figure, ASC has a pair of obvious redox peaks near 0.5 V, which indicates that the redox capacitance characteristics are effectively superimposed on the double-layer capacitance. When the current density increases, the shape of the CV curve changes slightly, indicating that ASC has a fast current potential response and charge-discharge performance.

[0019] Figure 5 b is the GCD test of HAQ-rGO / / MOC-rGO at different current densities. All GCD curves maintain good symmetry, which indicates that the capacitor has good electrochemical reversibility. At the same time, there is an obvious charge-discharge platform at around 0.4 V, which corresponds to the synergistic redox reaction of MOC-rGO and HAQ-rGO, which is consistent with the results of the CV curve. -1 The specific capacitance is 241.4 F•g -1 .

[0020] Figure 6 a is the relationship between the energy density and power density of HAQ-rGO / / MOC-rGO (ASC). The power density of this ASC is 600 W kg at a cell voltage of 1.6 V. -1 When the energy density is 68.83 Wh•kg -1 , when the power density is 5300 W•kg -1 When the energy density is 26.96 Wh•kg -1 .

[0021] Figure 6 b is the current density of the ASC at 3 A•g -1 Under the condition of high charge and discharge conditions, after 10,000 charge and discharge cycles, the capacitance retention rate was 90% and the coulombic efficiency was 100%, indicating that the ACS can still maintain stable energy storage after multiple cycles.

[0022] The utilization of energy storage and conversion technology of supercapacitor devices is of great significance for their practical applications. Therefore, we constructed supercapacitors HAQ-rGO / / MOC-rGO into devices and found that they could light up 60 LED bulbs and run a stopwatch for 52 minutes after being connected in series. Figure 7 shown.

[0023] In summary, the present invention fixes MOC on the rGO skeleton through a simple one-step solvothermal method to prepare a MOC-rGO composite electrode material. The present invention uses a non-covalent functionalization strategy to use reduced graphene oxide as a conductive substrate, selects a reversible electrochemically active organic molecule 3-methoxycatechol, and uses a solvothermal self-assembly method to fix it on the surface of reduced graphene oxide to prepare an organic molecule non-covalent functionalized graphene composite electrode material, and studies its actual energy storage performance. 3-methoxycatechol and reduced graphene oxide are reacted through non-covalent π-π interaction to prepare a composite electrode material MOC-rGO. The redox reaction of MOC on the surface of the carbon material rGO can increase not only the pseudocapacitance but also the total capacitance of the material. The experimental results show that the composite electrode material has good rate performance and cycle stability at a current density of 1 A•g -1 Under this condition, the specific capacitance of MOC-rGO is 427.9 F·g -1 In addition, the asymmetric supercapacitor composed of MOC-rGO and HAQ-rGO (HAQ-rGO / / MOC-rGO) has excellent energy storage performance, with energy density and power density of 68.83 Wh•kg -1 , 600 W•kg -1 , at a current density of 3 A•g -1 Under this condition, after 10,000 charge and discharge cycles, the capacitance retention rate is 90%. After being connected in series, it can light up 60 LED bulbs and make the stopwatch run for 52 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the synthesis of MOC-rGO composite materials.

[0025] Figure 2 SEM images of rGO (a and b) and SEM images of MOC-rGO (c and d).

[0026] Figure 3 Raman spectra of pure MOC and MOC-rGO.

[0027] Figure 4 (a) Pure MOC, rGO, and MOC-rGO at a scan rate of 10 mV s -1 CV curves of (a) MOC-rGO at different scan rates, (c) pure MOC, rGO and MOC-rGO at 1 A g -1 GCD curve of MOC-rGO at different current densities.

[0028] Figure 5(a) HAQ-rGO / / MOC-rGO at 1 MH at different scan rates 2 SO 4 CV curves in (a), (b) constant current charge and discharge curves of ASC at different current densities.

[0029] Figure 6 (a) Relationship between energy density and power density of HAQ-rGO / / MOC-rGO, (b) Relationship between energy density and power density of HAQ-rGO / / MOC-rGO at 3 A g -1 Cycle stability after 10,000 cycles.

[0030] Figure 7 The assembled ASC device illuminates 60 LEDs and runs a stopwatch for 52 minutes. DETAILED DESCRIPTION

[0031] The preparation method of the 3-methoxycatechol-modified reduced graphene oxide composite material of the present invention is further described in detail below in conjunction with specific examples. Example

[0032] 64 mg of graphene oxide was dispersed in 32 mL of double distilled water to obtain a graphene oxide dispersion. 16 mg of MOC and 32 mL of ethanol (C 2 H 5 OH) was mixed, and then graphene oxide dispersion was added. The solution was then transferred to a stainless steel autoclave and gradually heated to 180°C for 12 h. After the temperature dropped to room temperature, the black gel was carefully taken out with tweezers and then repeatedly washed with secondary water. Finally, the composite material MOC-rGO was obtained by freeze drying at -50°C for 24 h. MOC-rGO was tested at a current density of 1 A•g -1 Under this condition, the specific capacitance of MOC-rGO is 427.9 F·g -1 .

[0033] For structural characterization and performance evaluation, see above.

Claims

1. A method for preparing a 3-methoxycatechol-modified reduced graphene oxide composite material, characterized in that: First, graphene oxide is dispersed in double distilled water to obtain a graphene oxide dispersion, then 3-methoxycatechol and ethanol are mixed, and then the graphene oxide dispersion is added and mixed evenly. Then the mixed solution is transferred to a stainless steel high-pressure reactor, heated to 175-185°C and reacted for 10-14 hours. After the temperature drops to room temperature, it is washed and freeze-dried to obtain a 3-methoxycatechol-modified reduced graphene oxide composite material, recorded as MOC-rGO.

2. A method for preparing a 3-methoxycatechol-modified reduced graphene oxide composite material as claimed in claim 1, characterized in that: The mass ratio of 3-methoxycatechol to graphene oxide is 0.1:1~0.3:

1.

3. A method for preparing a 3-methoxycatechol-modified reduced graphene oxide composite material as claimed in claim 1, characterized in that: Freeze drying is the process of freeze drying at -50~-20℃ for 12~48h.

4. An application of the 3-methoxycatechol modified reduced graphene oxide composite material prepared by the method as claimed in claim 1 in a supercapacitor positive electrode material.

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